Recent advances in the field of additive manufacturing (AM) or 3D printing, have garnered serious interest for its potential to substitute time-consuming and costly subtractive and formative manufacturing techniques. Material extrusion (MatEx), employing filament and pelletbased feedstocks, is an AM technique for fabricating three-dimensional objects dictated by a computer-aided design (CAD) file in a layer-by-layer manner. Being inherently a "melt-and-form" technique, the physics of MatEx is strongly dependent on the melt flow behavior of the polymers and hence on their rheology. The focus of this review article is to analyze the current progress in rheological characterizations of filament and pellet-based polymeric feedstocks for application in MatEx. The importance of shear and temperature-dependent viscosities in relation to consistent extrusion through the print nozzle and in the standoff region between nozzle and bed will be highlighted. The importance of shear and/or extensional viscosities and extent of die swell (upon exit from the nozzle) experienced by the polymers under processing parameters relevant to MatEx will be investigated. Postextrusion from the nozzle, the rheological characteristics of the viscous polymer melt as it cools once deposited on the print bed governs the degree of interlayer welding, that impacts the mechanical performance of the printed parts. Controlling and monitoring rheological properties such as zero-shear viscosities and shear moduli of the melt is of significant importance in this region in order to ensure proper mechanical robustness and shape integrity of the deposited layers. Both experimental and theoretical approaches based on polymer chain reptation mechanisms will be reviewed in detail and suggestions to address the existing limitations associated with the process will be provided. Fundamental understanding of the correlation between the classical theories and current understanding based on recent experimentation and analysis is expected to assist the design and development of the next generation of polymer feedstocks and machine designs for MatEx-based AM.

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We report the plating and stripping of calcium metal at room temperature in a mixture of ethylene carbonate (EC) and propylene carbonate (PC) solvents using calcium tetrafluoroborate (Ca­(BF4)2) as the salt. Calcium is reversibly deposited and removed over several cycles, with associated plating–stripping efficiencies of >95%. Thin layers (∼20 μm) of crystalline calcium are present as the deposits, with a stable solid electrolyte interface (SEI) forming. This work opens opportunities to realize redox active Ca metal electrodes using commercially available alkyl carbonate solvents.

Calcium batteries are an emerging, next generation energy storage technology undergoing intense research toward viable operation. A key aspect in their development is plating and stripping of a calcium metal anode in suitable electrolytes. Herein, we report that calcium can be plated and stripped at room temperature in an ionic-liquid-based electrolyte. Thick continuous deposits (∼20 μm) of crystalline calcium are plated and stripped over 10 cycles to areal capacities of 2.2 mAh cm −2 at a current density of 0.56 mA/cm 2 . This work presents ionic liquids as viable electrolytes for calcium anodes to enable redox activity for calcium batteries.

We report on how polymer morphology is controlled through the self-trapping of transmitted optical beams in photoreactive polymer blends. Self-trapped optical beams, characterized by divergence-free propagation, drives the growth of a congruent arrangement of polymer filaments in the blends. With suitable component weight fractions and exposure intensity, binary phase morphologies form in precisely the same pattern as the beams’ arrangement, thereby producing 2D structures in polymer blend volumes of large depth and area. Morphology evolution and the formation processes were observed by in situ microscopy. In situ confocal Raman measurements of polymer conversion and molecular weight increase along the filament regions reveal that polymerization undergoes autoacceleration, followed by the onset of mixing instability which leads to phase separation. These phenomena begin at the front end of the filament and propagate along its length over the depth of the blend. Control over morphology is discussed with respect to the competitive processes of phase separation and photo-cross-linking.